The present invention relates to high performance instrumentation differential amplifiers in general, and more particularly to such an amplifier having a compensation channel to effect high common mode signal rejection.
Differential amplifiers are well known in the art and are used in many applications in which it is desired to amplify only the differential signal component of input signals having both differential signal components and common mode signal components. Examples of such applications include instrumentation amplifiers, physiological monitors, vertical amplifiers in oscilloscopes, and other measurment amplifiers. In such amplifiers, one measure of accuracy is the degree to which the common mode signal component can be cancelled or rejected, and this is known as common-mode rejection (CMR).
Many schemes have been attempted to improve the common-mode rejection characteristic of true differential amplifiers, including the use of elaborate guard circuits, feedback networks, capacitively-coupled bootstrapping networks, and power-supply regulation schemes. Common mode rejection of -120 dB has been attained through the use of such complex and expensive techniques; however, such techniques invariably impose some limitation upon the circuit, such as reduced bandwidth or dynamic range, which must be taken into consideration as possible trade-offs in optimizing common mode rejection in the design of differential amplifiers.